Behind the Image DIGITAL BREAST IMAGING ......• Other - plain text, HTML, HL7 CDA ? The Medicine...

The Medicine Behind the Image

DIGITAL BREAST IMAGING INFORMATICS:

CONSIDERATIONS FOR PACS ADMINISTRATORS

David Clunie, CTO, RadPharm, Inc.


Digital Breast Imaging

  Digital Mammography +/- CAD   Digital Breast Tomosynthesis (DBT)   Breast ultrasound – 2D and 3D   MRI – Dynamic Contrast +/- “CAD”   NM, PET, specific tracers   “Exotic” modalities – optical tomography


Mammography is

DIFFERENT !


Mammography Differences

  Very highly regulated – MQSA in US   Relatively poorly reimbursed   Screening is insensitive & non-specific   Screening -> mortality reduction   Frequently litigated   Short read times (esp. screening 1-2min)   Relatively large projection images



  Stylized reading process (hanging)   Pixel matrix exceeds display matrix   Features may be one pixel in size   Grayscale rendering is demanding   CAD is often used   Both raw and processed images needed   May need reprocessing



  May need extra views - wet read/recall   May need additional modality (US,MR)   May need biopsy   Priors are vital – film or (outside) digital   Must give patient CD / interpretable film   Lossy compression forbidden   Reporting stylized & letter required


Regulations - MQSA

  URL for MQSA questions: • http://www.fda.gov/CDRH/mammography/

robohelp/START.HTM

  E.g., under “Transfer of Records” …


Projection Image Size   One image

•  1914x2294 ≈ 4.2 MB •  3328x4096 ≈ 13 MB •  4095x5625 ≈ 22 MB

  Lossless compressed 5:1 •  From 0.84 to 4.4MB

  Four views, both For Processing and For Presentation (8 images) in one study •  33.6 to 176MB uncompressed •  6.7 to 35.2MB lossless compressed


Impact of Image Size

  Affects long term archive, interchange media   Impact on workstation performance

•  transfer from server to workstation (network) •  transfer from disk to RAM to frame buffer

  Users alternate between hanging steps •  tab back and forth between layouts instantly

  Work-list based pre-loading to disk/RAM •  next case ready and waiting instantly


Reading Process & Layout

  4 screening views L/R CC/MLO +/- prior   Flipped correctly back-to-back   +/- CAD marks   Overview (gestalt) on two monitors   Fit breast to screen – rest same size   Detailed comparison (1:1 pixels)   Film comparison (true-size)   Extra views (mustn’t be skipped)


Workstation Requirements

  Size - current and priors same size, fit to screen, true size

  Orientation - correctly flipped   Annotation - not on the breast; enough to QC   Justification - back-to-back with no gap   Grayscale contrast - as the vendor intended   Background air suppression - for windowing

& inversion

1:1 acquired to display pixel 5MP different sensors Original

1:1 acquired to display pixel 5MP different sensors Original Outline

1:1 acquired to display pixel 5MP different sensors Original Outline Boundary

1:1 acquired to display pixel 5MP different sensors Original Outline Boundary Fit Screen

Same size

Same size and fitted to screen


IHE Mammo Profile

  Defines the minimum display features required in all Image Display actors

  Defines what DICOM attributes shall be used to implement them

  Defines which DICOM Attributes the Acquisition Modality must populate

  Also addresses printing


Grayscale Contrast   Transform stored pixels to display values   Acquisition vendors use:

•  linear windowing •  sigmoid function windowing •  lookup table to encode function

  Unsatisfactory appearance if ignored   IHE profile requires support for all three   IHE also requires these be user adjustable   DICOM GSDF-calibrated display is required   Not burdensome for addition to typical PACS

Sigmoid curve encoded as specified shape with window parameters

0

500

1000

1500

2000

2500

3000

3500

4000

4500

1045

1130

1215

1300

1385

1470

1555

1640

1725

1810

1895

1980

2065

2150

2235

2320

2405

2490

2575

2660

2745

2830

2915

3000

3085

3170

3255

3340

3425

3510

3595

3680

3765

3850

3935

4020

Pixel Value (LUT Index)

P-V

alu

e

Window Width

Window Center


Layout and Annotation

  DICOM Mammo object uses codes •  for View and Modifier •  needed for flipping to A\F orientation •  needed for required standard label (“LMLOID”) •  e.g. Left MLO Implant displaced:

(“R-10226”,SRT,“MLO”) (“R-102D5”,SRT,“ID”)   General purpose viewers tend to hang based

on plain text (like series description)   Need mammography-specific programming

or scripting to support required functions


Annotation

  MQSA   ACR Quality Manual Requirements   Interpretation, QC and problem solving   Dose awareness   Must not overlay/obscure breast tissue   Gestalt impression during overview   Must not hide features under annotation


Series Organization

  Neither DICOM nor IHE defines Series •  each image may be separate series •  one series for set of four screening For Presentation

views •  four series with For Presentation and For

Processing pairs in one series for each view

  Robust viewer must not make assumptions about series organization

  IHE profile requires series independence


Workflow   Scheduled workflow for modality

•  IHE SWF +/- mammography specifics (new in 2008)

  CAD workflow •  de facto standard “push” workflow

  Reporting workflow •  no accepted standards

  Image distribution workflow •  IHE PDI

  Result distribution workflow •  no accepted standards

  Importation of priors workflow •  IHE IRWF


CAD

  Objective – improve sensitivity   Find and mark suspicious locations   Two primary informatics problems

• workflow – movement of images & results •  result encoding & display

  Results need to be visible during read


CAD “Push” Workflow   Acquisition modality produces

•  For Processing images -> CAD •  For Presentation images -> human reader

  CAD server •  passively receives images •  when to start CAD ? •  when to send CAD results ?

  Workstation (+/- PACS) displays •  For Presentation images •  with & without CAD marks •  when is exam “ready to read” (all images/CAD available) ?


Mammography

CAD Server

Workstation

For Processing

For Presentation

Mammography CAD


Mammography

Archive

CAD Server

Workstation

For Processing

For Presentation

Mammography CAD


Mammography

Archive

CAD Server

Workstation

For Processing

For Presentation

CAD Result

Manager

For Processing

For Presentation CAD Result


CAD Encoding   DICOM Structured Report

•  Mammography CAD SR SOP Class •  co-ordinates on For Processing image •  coded classification (mass, micro-calcification) •  required in all Image Displays by IHE •  format of displayed marks is not defined/encoded

  Support issues in non-IHE Image Display •  no support in “ordinary” viewers/PACS •  poor support – crash if SR too complicated •  poor filtering of complex content •  resolving UID reference to For Processing image


Non-IHE CAD Workarounds   Deployment

•  CAD server creates something else than SR CAD •  convertor box can change SR to something else

  Alternative encodings •  separate Presentation State object •  add 6000 overlay to new For Presentation image •  burned into pixels of another For Presentation image •  proprietary internal PACS annotation

  Issues with workarounds •  reader still needs to be able to turn marks on/off •  size/shape/behavior of marks may affect interpretation


CAD Archival   Additional issue of what to archive ?

•  input data (For Processing Images) •  CAD result itself

  Why archive ? •  reprocess next year -> better change detection •  “audit trail” to support decision making •  retrospective CAD supports interpretation (legal case) •  clinical trials

  Why not archive ? •  space (may matter for images, CAD size trivial) •  “audit trail” of decision with unfortunate outcome


For Processing/Presentation   DX family of objects, including mammo

•  For Presentation – processed, ready to view •  For Processing – raw, not viewable

  All modalities & displays •  shall support For Presentation •  may also support For Processing

  CAD requires For Processing   If user wants different (proprietary) processing

•  reprocess at modality •  send For Processing to (proprietary) workstation

  Interchange (media) requires >= For Presentation


Computed Radiography (CR)   Later to market in USA than fixed detectors   USA release supports DICOM MG   Separate devices expose and read cassettes   Makes it challenging to populate DICOM header

•  demographics, dates, IDs •  view and orientation •  technique and dose

  Vendor approaches •  bar coding •  retrofitting generator to acquire data

  User should still insist on IHE Mammo compliance


Compression

  Lossless compression only   No lossy compression for interpretation   No studies yet on lossy compression

• very encouraging results from digitized film • still no ROC study on FFDM data • confounded by different vendor

characteristics, detector size, processing • DMIST data set still sequestered and by now

probably obsolete


Lossless compression

  20 pairs (40 images) • of For Processing and For Presentation

  Three vendors • 4 pairs Lorad (1 patient, 4 views) • 4 pairs Fischer (1 patient, 4 views) • 12 pairs GE (3 patients, 4 views each)

Lossless Compression - Compression Ratios

0

1

2

3

4

5

6

7

Entrop

y

LGZIP

BGZIP

LCOMP

BCOMP

LBZ2

BBZ2

JPL1

JPL2

JPL3

JPL4

JPL5

JPL6

JPL7

JPEG

-LS

JPEG

200

0

Compression Scheme

Co

mp

ressio

n R

ati

o (

co

mp

ared

to

2 b

yte

s)

Both

For Presentation

For Processing


Lossless compression   For Presentation > For Processing

•  less noisy   All compress extremely well

•  mostly air   Considerable variation

•  size of breast   JPEG-LS and JPEG 2000 best

•  mean CR 6.27 and 6.25 For Presentation   Lossless JPEG (SV1) poor

•  mean CR 4.41 For Presentation •  no run length compression, so poor for large areas of air


Best - CR 12.9 Worst - CR 3.19

Variation in compressibility

JPEG-LS Lossless


Transfer between facilities   Special mammography requirements   Priors are essential   Combined film/softcopy undesirable   Women move (job, insurance, referrer)

  Therefore need standard, portable digital transport mechanism

  Nationwide/regional imaging network is long term   Portable digital media is currently the only answer


Media for mammography   Standard image format - DICOM Mammo Image

•  For Presentation only, or For Processing as well ?   Standard media - CD or DVD

•  How many images (visits) will fit ? Enough.   Compression

•  None, lossless (not lossy) ? Which scheme ? PDI - None   CAD

•  As DICOM Mammography CAD SR ? •  As DICOM Presentation State ? Both ?

  Radiologist’s reports and annotations •  DICOM Mammography SR ? •  Other - plain text, HTML, HL7 CDA ?


Media Viewers

  Many CD viewers not mammo aware   Suitability for referring doctor

•  e.g., surgeon for biopsy/lumpectomy   Support for localization of abnormality

•  Presentation States   Importation expectation avoids issue

•  surgeon’s own viewing system •  next year’s radiologist’s own workstation

  No proprietary formats & viewers !@#$


Printing

“For purposes of transferring films, the facility must be able to provide the medical institution, physician, healthcare provider, patient or patient’s representative, with hardcopy films of final interpretation quality or, when it is acceptable to the recipient (e.g., a transfer between two FFDM facilities), with original or lossless compressed full field digital images electronically.”

Questions about MQSA 900.12(c)(4)(ii),(iii)


Printing

  Must be able to print interpretation quality film   Physical size for hanging   True size, for biopsy, comparison as priors   Annotation, per MQSA and quality manual   Grayscale 12 bits and as per DICOM GSDF   Dmax sufficient for mammo (IHE > 3.5)   Insist on IHE Mammo profile for printing   Likely requires a dedicated mammo printer

with the appropriate film size(s)


Other modalities

  “Multi-modality” workstation   Isn’t that what a PACS workstation is ?   Breast ultrasound, same as any other   Breast MRI more difficult

•  dynamic contrast acquisition •  requires analysis of time-intensity curve •  so-called DCE-MR “CAD” application •  yet another non-integrated 3rd party device ? •  “plug-in” architecture – DICOM WG 23


Tomosynthesis   Multiple projection images   Reconstructed to make “slices”   And you thought FFDM images were big !   Impact of large size

•  archive and interchange media •  network retrieval on demand to disk and RAM (pre-fetch) •  speed of scrolling though slices •  20MB per slice, not 0.5MB CT, and 5MP display

  DICOM standard format ballot finished   Vendors may go to market with proprietary format   Demand DICOM in your contract in reasonable time


Conclusion   Mammography is different   3rd party workstations are capable, but not integrated

without reading worklist   PACS workstations are getting there   Insist on IHE Mammo profile, now or in reasonable

time per contract with penalties   Deploy CAD “properly”, with SR CAD   Archive everything, and do it losslessly   Produce DICOM/IHE PDI compliant media   Print interpretation quality films, true size, annotated   Prepare for tomo, and be afraid !


IHE Resources   IHE Mammography web site

•  http://www.ihe.net/Mammo/

  IHE Mammography Profile in Radiology TF •  http://www.ihe.net/Technical_Framework/

index.cfm#radiology

  Going Digital: An IHE Guide for Mammography •  http://www.ihe.net/Mammo/

going_digital_mammography.cfm

  IHE Mammography User's Handbook •  http://www.ihe.net/Resources/handbook.cfm

Behind the Image DIGITAL BREAST IMAGING ......• Other - plain text, HTML, HL7 CDA ? The Medicine...

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